DESCRIPTION: Crystallographic analysis will be carried out on two DNA polymerases of the "Pol I" family, E. coli DNA polymerase I and Thermus aquaticus (Taq) DNA polymerase, and Pol alpha class DNA polymerases from bacteriophages T4 and RB69. The aim is to understand the mechanism of fidelity in structural terms, and towards this end, the structures of template-primer and dNTP complexes will be determined. For the bacteriophage proteins, the structures of complexes of the polymerase with single stranded DNA binding protein and the processivity factor will be pursued.